Mobile communication devices, such as smart phones and tablet computers have become essentials in the modern life. A time-division duplex long term evolution (TDD-LTE) standard is one of the latest wireless communication system configurations. In a TDD-LTE system, a mobile communication device of a user is referred to as a user equipment (UE). A technique of orthogonal frequency-division multiplexing (OFDM) is adopted for signal generation of the TDD-LTE. One of the OFDM features lies in transmission using a plurality of sub-carriers, and these sub-carriers correspond to a serving cell.
In a TDD-LTE system, downlink information from a base station may be received by a UE through one or more serving cells, or uplink information may be transmitted to the base station from a UE. Time resources for each serving cell are partitioned chronologically as a plurality of frames. Each frame is partitioned as 10 subframes, and subframes in each frame are numbered 0 through 9. Each frame includes three types of subframes, which are downlink subframe (DL subframe), uplink subframe (UL subframe) and special subframe. Table 1 below illustrates various types of UL-DL configurations of the TDD-LTE standard.
TABLE 1UL-DL configurations of the TDD-LTE standardUL-DLSubframe No.configuration01234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
Table 1 lists seven types of UL-DL configurations of the TDD-LTE standard, which are numbered 0 through 6. Depending on requirements, the base station may determine an UL-DL configuration corresponding to a serving cell for setting a subframe type for the serving cell. In Table 1, each box under subframe Nos. 0 through 9 represents a subframe, wherein D, S or U respectively represents that the subframe is defined as a DL subframe, a special subframe, or an UL subframe. For example, when the base station determines a certain serving cell to adopt UL-DL configuration 3, subframe No. 0 of the serving cell is defined as a DL subframe, subframe No. 1 is defined as a special subframe, subframe Nos. 2 through 4 are defined as UL subframes, and subframe Nos. 5 through 9 are defined as DL subframes, and the other UL-DL configurations do so likewise. The special subframe (S) has several configurations provided for the base station to determine whether to transmit downlink information in the subframe to the UE. If the configurations of the subframe can support to transmit downlink information to the UE, then the special subframe may simply considered as a DL subframe (D) in the disclosure. Thus, UL/DL ratio of the UL-DL configurations may be configured as from 2:3 to 9:1 and so on. The base station determines the UL-DL configuration used by the serving cell according to the UL/DL ratio required by the UEs served by one serving cell.
The HARQ is a mechanism used for increasing information transmission efficiency in a wireless communication system. In such mechanism, if information in a DL subframe can be successfully received by a UE from the base station, the UE reports a corresponding positive acknowledgement (ACK) to the base station. If, due to certain reasons such as bad communication quality, information in a DL subframe cannot be successfully received by a UE from the base station, the UE reports a corresponding negative acknowledgement (NACK) to the base station. When a NACK is received by the base station, the information corresponding to the NACK will be transmitted again to the UE sending the NACK. The aforementioned ACK and the NACK are collectively referred to as HARQ-ACK.
HARQ-ACK reporting is regulated by a certain time requirement. Some UL subframes have corresponding downlink (DL) association sets thereof. The DL association set is composed of at least one DL subframe chronologically before the UL subframe in the same serving cell. If downlink information from base station is received by a UE in a DL association set corresponding to a UL subframe, the UE has to perform the HARQ-ACK report regarding the downlink information to the base station in the UL subframe.
Table 2 below illustrates corresponding relationship between an UL subframe and a DL association set of each UL-DL configuration. FIG. 1A through FIG. 1G are schematic diagrams illustrating the corresponding relationship between the UL subframe and the DL association set of a TDD-LTE system.
TABLE 2The schematic diagram of the corresponding relationship between the ULsubframe and the DL association set of the TDD-LTE system.UL-DLSubframe No.configuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8,———————7, 5, 4, 11, 66——775——77—
Each row in Table 2 corresponds to a UL-DL configuration, i.e. UL-DL configurations 0 through 6, respectively, and each line in Table 2 corresponds to a subframe, i.e. subframe Nos. 0 through 9. If a grid shows “-”, it represents that a corresponding subframe thereof is a DL subframe or an UL subframe having no corresponding DL association set. If a grid shows one or more digits, each of the digits indicates that a location of a DL subframe in a DL association set, and the locations of the DL subframes are also illustrated in FIG. 1A through FIG. 1G. FIG. 1A through FIG. 1G correspond to the UL-DL configurations 0 through 6, respectively.
In FIG. 1A through FIG. 1G, two frames are illustrated, respectively. A vertical dotted line in the center as illustrated in each diagram represents a separation of the two sequential frames. For example, a vertical dotted line 110 in the center as illustrated in FIG. 1A is a separation of two sequential frames based on UL-DL configuration 0. Grids of the row on top in FIG. 1A through FIG. 1G represents the same UL-DL configurations as Table 1, while grids of each row under the UL-DL configurations illustrates an UL subframe and its corresponding DL association set, wherein the UL subframe is labeled as “A”, and “A” represents the acknowledgement(s) to be reported by the UE. Each DL subframe of the DL association set is labeled as “D”. The corresponding relationship of the UL subframes and their DL association sets is also illustrated in Table 2.
Taking the UL-DL configuration 0 depicted in FIG. 1A for example, one DL subframe is included in the DL association set of the UL subframe 2, i.e. the sixth subframe chronologically before the UL subframe 2. One DL subframe is included in the DL association set of the UL subframe 4, i.e. the fourth subframe chronologically before the UL subframe 4. One DL subframe is included in the DL association set of the UL subframe 7, i.e. the sixth subframe chronologically before the UL subframe 7. One DL subframe is included in the DL association set of the UL subframe 9, i.e. the fourth subframe chronologically before the UL subframe 9.
Taking the UL-DL configuration 1 depicted in FIG. 1B for example, two DL subframes are included in the DL association set of the UL subframe 2, i.e. the sixth and the seventh subframes chronologically before the UL subframe 2, respectively. One DL subframe is included in the DL association set of the UL subframe 3, i.e. the fourth subframe chronologically before the UL subframe 3. Two DL subframes are included in the DL association set of the UL subframe 7, i.e. the sixth and the seventh subframes chronologically before the subframe 7. One DL subframe is included in the DL association set of the UL subframe 8, i.e. the fourth subframe chronologically before the UL subframe 8.
Taking the UL-DL configuration 2 depicted in FIG. 1C for example, four DL subframes are included in the DL association set of the UL subframe 2, i.e. the fourth and the sixth through the eighth subframes chronologically before the UL subframe 2, respectively. Samely, four DL subframes are included in the DL association set of the UL subframe 7, i.e. the fourth and the sixth through the eighth subframes chronologically before the UL subframe 7.
UL-DL configurations 3 through 6 are illustrated likewise in FIG. 1D through FIG. 1G, which can be inferred based on above examples and will not be repeatedly described hereinafter.
FIG. 2A and FIG. 2B are schematic diagrams of the DL subframes and the subframes of the aforementioned TDD-LTE system. When a base station intents to transmit downlink information to a UE, as shown in FIG. 2A, the base station uses a DL subframe 210 for downlink assignment. The base station first transmits a physical downlink control channel (PDCCH) 211 in the DL subframe 210 and then, transmits a physical downlink shared channel (PDSCH) 213. The PDCCH 211 includes downlink assignment downlink control information (DL assignment DCI) 212, which is used for informing the UE that downlink information from the base station is waiting for being received by the UE in the PDSCH 213.
Among the PDSCHs received by the UE from the base station, some PDSCHs may be used for broadcasting of system information, and it is not required for the UE to perform the HARQ-ACK report for receiving such PDSCHs. For any UE, the HARQ-ACK report is necessary to inform base station whether the downlink information can be successfully received only when the UE receives UE-specific downlink information.
If the PDSCH 213 of the DL subframe 210 is a UE-specific PDSCH, then the DL assignment DCI 212 includes a downlink assignment index, which is represented as VDAIDL hereinafter. VDAIDL is a value and transmitted to inform the UE of assigned numbers of such information in the DL subframe 210.
When the base station intents to assign uplink resource to a UE, as shown in FIG. 2B, the base station uses a DL subframe 220 for uplink grant. The base station transmits a PDCCH 221 in the DL subframe 220. The PDCCH 221 includes uplink grant downlink control information (UL grant DCI) 222. The UL grant DCI 222 is used for informing the UE that uplink information can be transmitted to the base station in a physical uplink shared channel (PUSCH) 231 of a following UL subframe 230. If the UE receives the downlink information via PDSCH in the DL subframe of the DL association set corresponding to the UL subframe 230, the UE is required to perform HARQ-ACK report of the DL subframes in the PUSCH 231. In addition, the UL grant DCI 222 includes a downlink assignment index WDAIUL. WDAIUL is a value and is transmitted to inform the UE that there are WDAIUL DL subframes whose HARQ-ACKs have to be reported in the PUSCH 231.
Carrier aggregation is a mechanism utilized for increasing the bandwidth of a wireless communication system. The UE supporting carrier aggregation may use a plurality of component carriers corresponding to a plurality of serving cells to transmit or receive information simultaneously so as to expand effective bandwidth for the UE.
FIG. 3 is a schematic diagram of a method of HARQ-ACK reporting applicable to a TDD-LTE system supporting the carrier aggregation. In the example as illustrated in FIG. 3, the UE may transmit or receive information simultaneously in three serving cells 320˜322, and the three serving cells 320˜322 use the same UL-DL configuration, i.e. the UL-DL configuration 2. Each of the serving cells 320˜322 are assigned a number c, which is 0, 1 and 2, respectively. In FIG. 3, five rows of grids are illustrated, wherein two frames based on the UL-DL configuration 2 are illustrated in the top row, while a subframe 301 and its corresponding DL association set are illustrated in the second row. Downlink information received by the UE in the serving cells 320˜322 and the HARQ-ACKs reported by the UE are respectively illustrated in the lower three rows.
The base station transmits downlink information via three DL subframes in the serving cell 320 to the UE, and the downlink assignment indexes VDAI,0DL of the three DL subframes are 1, 2 and 3, respectively. Due to bad communication quality, the downlink information of the first subframe is missed by the UE (the UE misses the detection of the corresponding downlink assignment DCI), and the grid is labeled with “X” in the diagram. Further, downlink information of the following two DL subframes can be received by the UE. The base station transmits the downlink information via two subframes in the serving cell 321 to the UE. The downlink assignment indexes VDAI,1DL of the two subframes are 1 and 2, respectively. The base station transmits downlink information via one subframe in the serving cell 322 to the UE. The downlink assignment index VDAI,2DL of the subframe is 1. Downlink information of the three subframes can be received by the UE in the serving cells 321 and 322.
In the TDD-LTE system supporting the carrier aggregation, acknowledgements of all serving cells are reported to the base station in a UL subframe via one of the serving cells. For example, in the example illustrated in FIG. 3, the base station provides an upload grant in a subframe 302 of the serving cell 320 (i.e. the last subframe of a DL association set of the subframe 301), specifies the UE to transmit uplink information according to the instruction of the uplink grant in the subframe 301 of the serving cell 320 and reports all HARQ-ACKs of the three serving cells 320˜322. The base station also provides a downlink assignment index WDAIUL to the UE in the uplink grant of the subframe 302 of the serving cell 320. Differing from the scenario of only single serving cell, when there is a plurality of serving cells, WDAIUL is applicable to each serving cell, and in the example illustrated in FIG. 3, WDAIUL is equal to 3.
In the example illustrated in FIG. 3, the UE uses a configuration of a physical uplink control channel format 3 (PUCCH format 3) in the PUSCH of the UL subframe 301 of the serving cell 320 to report the HARQ-ACK. The UE have to report HARQ-ACKs of WDAIUL subframes for each serving cell. Taking the example illustrated in FIG. 3 for instance, HARQ-ACKs of nine DL subframes in total is required to be reported, which may be represented as [AN0,1, AN0,2, AN0,3, AN1,1, AN1,2, AN1,3, AN2,1, AN2,2, AN2,3], wherein [AN0,1, AN0,2, AN0,3] are HARQ-ACKs of three DL subframes of the serving cell 320. Since information of the first DL subframe is missed by the UE, AN0,1 represents a negative ACK of a missed reception, while AN0,2 and AN0,3 are HARQ-ACKs representing whether downlink information is successfully received. [AN1,1, AN1,2, AN1,3] are HARQ-ACKs of the three DL subframes of the serving cell 321. Since the base station actually transmits downlink information via two DL subframes in the serving cell 321, while AN1,1, and AN1,2 are HARQ-ACKs representing whether the information is successfully received, and AN1,3 is a negative ACK representing no downlink information. [AN2,1, AN2,2, AN2,3] are HARQ-ACKs of three DL subframes of the serving cell 322. Since the base station actually transmits downlink information of a subframe only in the serving cell 322, AN3,1 is the HARQ-ACK representing whether the downlink information has been successfully received, while AN3,2 and AN3,3 are negative ACKs representing no downlink information.